1. Field of the Invention
The present invention relates generally to the oil and gas field, and more specifically, to an open top tank with tandem diffusers that decrease the velocity and pressure of the fracturing fluid or flowback from the well.
2. Description of the Related Art
Hydraulic fracturing is the process by which high-pressure fluids are used to create small fractures in a formation in order to stimulate production from new and existing oil and gas wells. Fractures in the formation are created by pumping large quantities of fluids at high pressure down a wellbore and into the target formation. This fracturing fluid is mostly water but also includes proppant (typically in the form of conventional sand or ceramic sand) and chemical additives. The proppant consists of small, granular substances that hold the newly created fractures open. The viscosity of the fracturing fluid is important, and to this end, gels or other friction reducers may be added to bring the fracturing fluid to the desired viscosity.
When the injection process is completed, the internal pressure of the formation causes fluid to return to the surface through the wellbore. This fluid is referred to herein as “flowback,” which contains water, proppant, gels and chemicals. The flowback may also include groundwater and natural gas, as well as other naturally occurring materials such as brines, metals, radionuclides, and hydrocarbons. In a typical scenario, the flowback flows to the surface first, followed by the oil and gas recovered from the fractured formation. Because the delineation between the flowback and the profitable material (oil and gas) is not precise, the flowback often contains oil and gas as well.
Once it reaches the surface, the flowback must be treated, recycled and/or disposed of. Before any one of these processes can take place, the flowback must be stored temporarily (in a tank or pit). Preferably, the proppant (sand) is eliminated from the flowback before it is transported (via above-ground pipes) to any other process. At high pressures, the abrasive qualities of solids (sand, formation rock, etc.) in the flowback wears away the pipe through which the flowback travels. Over time, these wear points may eventually coalesce, causing complete erosion of the pipe. This kind of event often results in severe environmental and property damage and may cause serious bodily injury or death. In addition, because the flowback exits the wellbore at such high velocity and pressure, it is desirable to decrease both the velocity and the pressure of the flowback before it is sent to the next stage in processing.
One method that has been devised to deal with the velocity and pressure of the flowback is to provide (either in a tank or in a pipe) baffles or plates that extend downward or upward from the inside surface of the tank/pipe. These baffles or plates are typically (but not always) angled (i.e., not perpendicular to the inside surface of the tank/pipe) and alternate up/down (i.e., upwardly extending plate, downwardly extending plate, upwardly extending plate, etc.). The problem with this design is that the flowback hits these plates and eventually causes them to fail due to targeted and repeated wear. Also, there is no method for removing the proppant from the flowback, separating out the oil and gas from the flowback, or recovering the clean water.
For the reasons explained above, it is an object of the present invention to provide a tank for storing flowback before it is transported to the next stage in the process. It is a further object of the present invention to reduce both the velocity and the pressure of the flowback. Yet another object of the present invention is to remove the proppant from the flowback. The present invention not only accomplishes these objectives but also separates the oil from the flowback and allows the clean water to be recovered.